1. Field of the Invention
The present invention relates to magnetic heads that record data by applying a magnetic field to a magnetic recording medium and, in particular, relates to a magnetic head that works with a high-frequency recording signal and accommodates the implementation a narrow recording-track design.
2. Description of the Related Art
FIG. 19 is a sectional view of a known magnetic head. The magnetic head is an inductive head that guides a magnetic field, generated by a coil layer to which a signal current is supplied, to an upper core layer and a lower core layer, and generates a leakage magnetic field from a non-magnetic gap layer provided between the upper core layer and the lower core layer.
In the magnetic head shown in FIG. 19, a Gd determining layer 11, made of a non-magnetic material, is disposed a lower core layer 10. A magnetic pole section 12 is provided from a face opposing a recording medium to the Gd determining layer 11. The magnetic pole section 12 includes a laminate of a lower magnetic pole layer 13, a non-magnetic gap layer 14, and an upper magnetic pole layer 15. The magnetic pole section 12 has a width dimension of track width Tw (in a direction of X as shown).
An insulating layer 16 is disposed on both sides of the magnetic pole section 12 in the track width direction (the X direction) and in a height direction (in the Y direction as shown). The top surface of the insulating layer 16 is flush with the top surface of the magnetic pole section 12.
As shown in FIG. 19, a coil layer 17 is provided in a spiral pattern on the insulating layer 16. The coil layer 17 is covered with an insulating layer 18 made of an organic insulating material.
An upper core layer 19 is provided on the magnetic pole section 12 and the insulating layer 18. A base portion 19a of the upper core layer 19 is directly connected to a junction layer (back gap layer) 20, made of a magnetic material, and disposed on the lower core layer 10. In the known magnetic head shown in FIG. 19, a thickness t2 at an apex thereof is larger than a thickness t1 at the leading edge of the upper core layer 19.
In the magnetic head shown in FIG. 19, the insulating layer 18 covering the coil layer 17 has a slope surface 18a facing the recording medium. The upper core layer 19 has a yoke structure provided on the slope surface 18a of the insulating layer 18.
To implement high recording density in an inductive head, overwrite characteristics (OW) must be improved. To improve the OW characteristics, saturation magnetic flux densities in the upper core layer 19, the upper magnetic pole layer 15, the lower magnetic pole layer 13, the lower core layer 10, and the back gap layer 20 are preferably high. A magnetic field generated by the coil layer 17 passes through the upper core layer 19, the upper magnetic pole layer 15, the lower magnetic pole layer 13, the lower core layer 10, and the back gap layer 20.
To heighten a line recording density, the frequency of a recording signal supplied to the inductive head must be increased. However, if the recording signal frequency becomes high, eddy currents occurring in the upper core layer 19 and the lower core layer 10 increase, and an eddy current loss becomes larger accordingly.
Each of the lower core layer 10 and the upper core layer 19 is made of a nickel-iron (NiFe) alloy. To reduce the eddy current, the use of a magnetic material having a high specific resistance, such as FeNiMo, for the upper core layer 19 and the lower core layer 10 has been proposed as disclosed in Japanese Unexamined Patent Application No. 8-212512 (pages 11–12 and FIGS. 16–18), Japanese Unexamined Patent Application Publication No. 9-63016 (pages 5–6 and FIG. 5), Japanese Unexamined Patent Application Publication No. 2000-235911 (pages 3–4 and FIG. 1), and Japanese Unexamined Patent Application Publication No. 2001-76315 (pages 8–9 and FIG. 1).
If the entire upper core layer 19 is merely made of a magnetic material having a high specific resistance, the concentration of an element responsible for magnetization (such as iron) is reduced. The upper core layer 19 provides an insufficient saturation magnetic flux density.
If each of the upper core layer 19 and the lower core layer 10 is produced in a laminate structure in which a layer of a magnetic material having a high specific resistance and a low saturation magnetic flux density and a layer of a magnetic material having a low specific resistance and a high saturation magnetic flux density are laminated, magnetic flux is disturbed in an interface between the two layers.